As is known in the art, in many applications it is desired to detect both infrared and ultraviolet radiation from an object or distinguish between two different objects at a common pixel of an array of detector elements; sometimes referred to as dual band UV and Infrared (IR) radiation detectors. One such detector is shown in FIG. 1 to include an infrared detector, here of Indium-Antimonide, mounted below a semiconductor, ultraviolet radiation detector, such as Cadmium Sulfide (CdS) bulk crystal approximately 0.5 mm thick, as shown (or Cadmium Selenide (CdSe) or Cadmium Telluride CdTe); the ultraviolet detector having the bottom surface epoxied with an IR transparent epoxy, to a filter, here silicon, for passing infrared energy passing through the ultraviolet detector to the infrared detector. It is noted that a Schottky contact is formed on the upper surface of the CdS, forming a Schottky barrier region approximately 10 nm thick. One such UV detector is a Schottky barrier photovoltaic detector described in U.S. Pat. No. 4,319,258 issued Mar. 9, 1982, inventors Harnagel et al. Here, a metal electrode, such as platinum (Pt) and gold (Au), interacts through proper reaction with CdS interface to form a Schottky bather rectifying junction. As described therein a slice is taken from a single crystalline cadmium sulfide ingot designated as being of the N-type with a preferred orientation for slicing the wafer such that the c-axis of the hexagonal crystal is perpendicular to the surface of the wafer. The wafer is next etched in a solution of hydrochloric acid to identify the positive and negative orientation sides of the wafer. The wafer is then mounted on a work fixture and lapped flat to a suitable thickness. Following the lapping operation, the wafer is polished. The wafer is then processed to form an infrared shield on the upper surface of the cadmium sulfide substrate which is chosen so that it is the cadmium-rich side of the wafer. Preferably, the infrared shield structure is composed of a layer gold which is opaque to infrared radiation, sandwiched between thin layers of an adhesion metal. The adhesion metal is preferably titanium but it also may be aluminum, magnesium, zirconium, hafnium, or alloys of various combinations thereof. Preferably, the layer of gold is sandwiched between two relatively thin layers of titanium. Also, acid etching had to be performed to prepare the Schottky surface layer for correct electrical performance.
As is also known in the art, Cadmium Sulfide-Schottky contact junctions have been discussed in a paper entitled Rectifying Contacts Under Evaporated CdS” by JOHN A. SCOTT-MONCK ARTHUR J. LEARN, published PROCEEDINGS OF THE IEEE, JANUARY 1968 page 68.